diff --git a/Documentation/acpi/initrd_table_override.txt b/Documentation/acpi/initrd_table_override.txt
index 35c3f54..eb651a6 100644
--- a/Documentation/acpi/initrd_table_override.txt
+++ b/Documentation/acpi/initrd_table_override.txt
@@ -1,5 +1,5 @@
-Overriding ACPI tables via initrd
-=================================
+Upgrading ACPI tables via initrd
+================================
 
 1) Introduction (What is this about)
 2) What is this for
@@ -9,12 +9,14 @@ Overriding ACPI tables via initrd
 1) What is this about
 ---------------------
 
-If the ACPI_INITRD_TABLE_OVERRIDE compile option is true, it is possible to
-override nearly any ACPI table provided by the BIOS with an instrumented,
-modified one.
+If the ACPI_TABLE_UPGRADE compile option is true, it is possible to
+upgrade the ACPI execution environment that is defined by the ACPI tables
+via upgrading the ACPI tables provided by the BIOS with an instrumented,
+modified, more recent version one, or installing brand new ACPI tables.
 
-For a full list of ACPI tables that can be overridden, take a look at
-the char *table_sigs[MAX_ACPI_SIGNATURE]; definition in drivers/acpi/osl.c
+For a full list of ACPI tables that can be upgraded/installed, take a look
+at the char *table_sigs[MAX_ACPI_SIGNATURE]; definition in
+drivers/acpi/tables.c.
 All ACPI tables iasl (Intel's ACPI compiler and disassembler) knows should
 be overridable, except:
    - ACPI_SIG_RSDP (has a signature of 6 bytes)
@@ -25,17 +27,20 @@ Both could get implemented as well.
 2) What is this for
 -------------------
 
-Please keep in mind that this is a debug option.
-ACPI tables should not get overridden for productive use.
-If BIOS ACPI tables are overridden the kernel will get tainted with the
-TAINT_OVERRIDDEN_ACPI_TABLE flag.
-Complain to your platform/BIOS vendor if you find a bug which is so sever
-that a workaround is not accepted in the Linux kernel.
+Complain to your platform/BIOS vendor if you find a bug which is so severe
+that a workaround is not accepted in the Linux kernel. And this facility
+allows you to upgrade the buggy tables before your platform/BIOS vendor
+releases an upgraded BIOS binary.
 
-Still, it can and should be enabled in any kernel, because:
-  - There is no functional change with not instrumented initrds
-  - It provides a powerful feature to easily debug and test ACPI BIOS table
-    compatibility with the Linux kernel.
+This facility can be used by platform/BIOS vendors to provide a Linux
+compatible environment without modifying the underlying platform firmware.
+
+This facility also provides a powerful feature to easily debug and test
+ACPI BIOS table compatibility with the Linux kernel by modifying old
+platform provided ACPI tables or inserting new ACPI tables.
+
+It can and should be enabled in any kernel because there is no functional
+change with not instrumented initrds.
 
 
 3) How does it work
@@ -50,23 +55,31 @@ iasl -d *.dat
 # For example add this statement into a _PRT (PCI Routing Table) function
 # of the DSDT:
 Store("HELLO WORLD", debug)
+# And increase the OEM Revision. For example, before modification:
+DefinitionBlock ("DSDT.aml", "DSDT", 2, "INTEL ", "TEMPLATE", 0x00000000)
+# After modification:
+DefinitionBlock ("DSDT.aml", "DSDT", 2, "INTEL ", "TEMPLATE", 0x00000001)
 iasl -sa dsdt.dsl
 # Add the raw ACPI tables to an uncompressed cpio archive.
-# They must be put into a /kernel/firmware/acpi directory inside the
-# cpio archive.
-# The uncompressed cpio archive must be the first.
-# Other, typically compressed cpio archives, must be
-# concatenated on top of the uncompressed one.
+# They must be put into a /kernel/firmware/acpi directory inside the cpio
+# archive. Note that if the table put here matches a platform table
+# (similar Table Signature, and similar OEMID, and similar OEM Table ID)
+# with a more recent OEM Revision, the platform table will be upgraded by
+# this table. If the table put here doesn't match a platform table
+# (dissimilar Table Signature, or dissimilar OEMID, or dissimilar OEM Table
+# ID), this table will be appended.
 mkdir -p kernel/firmware/acpi
 cp dsdt.aml kernel/firmware/acpi
-# A maximum of: #define ACPI_OVERRIDE_TABLES 10
-# tables are  currently allowed (see osl.c):
+# A maximum of "NR_ACPI_INITRD_TABLES (64)" tables are currently allowed
+# (see osl.c):
 iasl -sa facp.dsl
 iasl -sa ssdt1.dsl
 cp facp.aml kernel/firmware/acpi
 cp ssdt1.aml kernel/firmware/acpi
-# Create the uncompressed cpio archive and concatenate the original initrd
-# on top:
+# The uncompressed cpio archive must be the first. Other, typically
+# compressed cpio archives, must be concatenated on top of the uncompressed
+# one. Following command creates the uncompressed cpio archive and
+# concatenates the original initrd on top:
 find kernel | cpio -H newc --create > /boot/instrumented_initrd
 cat /boot/initrd >>/boot/instrumented_initrd
 # reboot with increased acpi debug level, e.g. boot params:
diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index 82b96ee..b225c4b 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -311,12 +311,12 @@ config ACPI_CUSTOM_DSDT
 	bool
 	default ACPI_CUSTOM_DSDT_FILE != ""
 
-config ACPI_INITRD_TABLE_OVERRIDE
-	bool "ACPI tables override via initrd"
+config ACPI_TABLE_UPGRADE
+	bool "Allow upgrading ACPI tables via initrd"
 	depends on BLK_DEV_INITRD && X86
-	default n
+	default y
 	help
-	  This option provides functionality to override arbitrary ACPI tables
+	  This option provides functionality to upgrade arbitrary ACPI tables
 	  via initrd. No functional change if no ACPI tables are passed via
 	  initrd, therefore it's safe to say Y.
 	  See Documentation/acpi/initrd_table_override.txt for details
diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index 2e74dbf..08795fb 100644
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -442,7 +442,7 @@ static void acpi_table_taint(struct acpi_table_header *table)
 	add_taint(TAINT_OVERRIDDEN_ACPI_TABLE, LOCKDEP_NOW_UNRELIABLE);
 }
 
-#ifdef CONFIG_ACPI_INITRD_TABLE_OVERRIDE
+#ifdef CONFIG_ACPI_TABLE_UPGRADE
 static u64 acpi_tables_addr;
 static int all_tables_size;
 
@@ -471,9 +471,9 @@ static const char * const table_sigs[] = {
 
 #define ACPI_HEADER_SIZE sizeof(struct acpi_table_header)
 
-#define ACPI_OVERRIDE_TABLES 64
-static struct cpio_data __initdata acpi_initrd_files[ACPI_OVERRIDE_TABLES];
-static DECLARE_BITMAP(acpi_initrd_installed, ACPI_OVERRIDE_TABLES);
+#define NR_ACPI_INITRD_TABLES 64
+static struct cpio_data __initdata acpi_initrd_files[NR_ACPI_INITRD_TABLES];
+static DECLARE_BITMAP(acpi_initrd_installed, NR_ACPI_INITRD_TABLES);
 
 #define MAP_CHUNK_SIZE   (NR_FIX_BTMAPS << PAGE_SHIFT)
 
@@ -488,7 +488,7 @@ static void __init acpi_table_initrd_init(void *data, size_t size)
 	if (data == NULL || size == 0)
 		return;
 
-	for (no = 0; no < ACPI_OVERRIDE_TABLES; no++) {
+	for (no = 0; no < NR_ACPI_INITRD_TABLES; no++) {
 		file = find_cpio_data(cpio_path, data, size, &offset);
 		if (!file.data)
 			break;
@@ -611,19 +611,30 @@ acpi_table_initrd_override(struct acpi_table_header *existing_table,
 		table_length = table->length;
 
 		/* Only override tables matched */
-		if (test_bit(table_index, acpi_initrd_installed) ||
-		    memcmp(existing_table->signature, table->signature, 4) ||
+		if (memcmp(existing_table->signature, table->signature, 4) ||
+		    memcmp(table->oem_id, existing_table->oem_id,
+			   ACPI_OEM_ID_SIZE) ||
 		    memcmp(table->oem_table_id, existing_table->oem_table_id,
 			   ACPI_OEM_TABLE_ID_SIZE)) {
 			acpi_os_unmap_memory(table, ACPI_HEADER_SIZE);
 			goto next_table;
 		}
+		/*
+		 * Mark the table to avoid being used in
+		 * acpi_table_initrd_scan() and check the revision.
+		 */
+		if (test_and_set_bit(table_index, acpi_initrd_installed) ||
+		    existing_table->oem_revision >= table->oem_revision) {
+			acpi_os_unmap_memory(table, ACPI_HEADER_SIZE);
+			goto next_table;
+		}
 
 		*length = table_length;
 		*address = acpi_tables_addr + table_offset;
-		acpi_table_taint(existing_table);
+		pr_info("Table Upgrade: override [%4.4s-%6.6s-%8.8s]\n",
+			table->signature, table->oem_id,
+			table->oem_table_id);
 		acpi_os_unmap_memory(table, ACPI_HEADER_SIZE);
-		set_bit(table_index, acpi_initrd_installed);
 		break;
 
 next_table:
@@ -655,17 +666,26 @@ static void __init acpi_table_initrd_scan(void)
 		table_length = table->length;
 
 		/* Skip RSDT/XSDT which should only be used for override */
-		if (test_bit(table_index, acpi_initrd_installed) ||
-		    ACPI_COMPARE_NAME(table->signature, ACPI_SIG_RSDT) ||
+		if (ACPI_COMPARE_NAME(table->signature, ACPI_SIG_RSDT) ||
 		    ACPI_COMPARE_NAME(table->signature, ACPI_SIG_XSDT)) {
 			acpi_os_unmap_memory(table, ACPI_HEADER_SIZE);
 			goto next_table;
 		}
+		/*
+		 * Mark the table to avoid being used in
+		 * acpi_table_initrd_override(). Though this is not possible
+		 * because override is disabled in acpi_install_table().
+		 */
+		if (test_and_set_bit(table_index, acpi_initrd_installed)) {
+			acpi_os_unmap_memory(table, ACPI_HEADER_SIZE);
+			goto next_table;
+		}
 
-		acpi_table_taint(table);
+		pr_info("Table Upgrade: install [%4.4s-%6.6s-%8.8s]\n",
+			table->signature, table->oem_id,
+			table->oem_table_id);
 		acpi_os_unmap_memory(table, ACPI_HEADER_SIZE);
 		acpi_install_table(acpi_tables_addr + table_offset, TRUE);
-		set_bit(table_index, acpi_initrd_installed);
 next_table:
 		table_offset += table_length;
 		table_index++;
@@ -689,7 +709,7 @@ acpi_table_initrd_override(struct acpi_table_header *existing_table,
 static void __init acpi_table_initrd_scan(void)
 {
 }
-#endif /* CONFIG_ACPI_INITRD_TABLE_OVERRIDE */
+#endif /* CONFIG_ACPI_TABLE_UPGRADE */
 
 acpi_status
 acpi_os_physical_table_override(struct acpi_table_header *existing_table,
